Preview Maker reads all the files in the directory you specify, and writes a preview file for every image it finds.

Where does Preview Maker put the previews?

Preview Maker reads every file in the folder you specify, optionally including subfolders, too. For any image files it finds, it creates a preview image file with the same name, and writes it in a subdirectory named something like "Previews256x128". (Where 256 and 128 are the maximum width and height you selected for the previews.)